Surface-modified, pyrogenically produced mixed oxides, method of their production and use

ABSTRACT

Surface-modified, pyrogenically produced mixed oxides which contain two or more components of the series SiO 2 , Al 2  O 3 , TiO 2 , ZrO 2 , Fe 2  O 3 , Nb 2  O 5 , V 2  O 5 , WO 3 , SnO 2 , GeO 2  and have been surface-modified with one to several compounds of the following groups: 
     (a) organosilanes of the type (RO) 3  Si(C n  H 2n+1 ), 
     (b) R&#39; x  (RO) y  Si(C n  H 2n+1 ), 
     (c) X 3  Si(C n  H 2n+1 ), 
     (d) X 2  (R&#39;)Si(C n  H 2n+1 ), 
     (e) X(R&#39;) 2  Si(C n  H 2n+1 ), 
     (f) (RO) 3  Si(CH 2 ) m  --R&#39;, 
     (g) (R&#34;) x  (RO) y  Si(CH 2 ) m  --R&#39;, 
     (h) X 3  Si(CH 2 ) m  --R&#39;, 
     (i) (R)X 2  Si(CH 2 ) m  --R&#39;, 
     (j) (R) 2  X Si(CH 2 ) m  --R&#39;, 
     (k) Silazanes of the type ##STR1## (l) Cyclic polysiloxanes, (m) Polysiloxanes or silicone oils.

FIELD OF THE INVENTION

The invention relates to surface-modified, pyrogenically produced mixed oxides and methods of their production and use.

BACKGROUND INFORMATION SUMMARY OF THE INVENTION

Subject matter of the invention constitutes surface-modified, pyrogenically produced mixed oxides which contain two or more components of the series SiO₂, Al₂ O₃, TiO₂, ZrO₂, Fe₂ O₃, Nb₂ O₅, V₂ O₅, WO₃, SnO₂, GeO₂ and were surface-modified with one or several compounds of the following groups:

(a) Organosilanes of the type (RO)₃ Si(C_(n) H_(2n+1))

R=alkyl, such as e.g. methyl-, ethyl-, n-propyl-, i-propyl-, butyl--

n=1-20

(b) Organosilanes of the type R'_(x) (RO)_(y) Si(C_(n) H_(2n+1))

R=alkyl, such as e.g. methyl-, ethyl-, n-propyl-, i-propyl-, butyl--

R=alkyl such as e.g. methyl-, ethyl-, n-propyl-, i-propyl-, butyl--

n=1-20

x=y=3

x=1, 2

y=1, 2

(c) Halogenorganosilanes of the type X₃ Si(C_(n) H_(2n+1))

X=Cl, Br

n=1-20

(d) Halogenorganosilanes of the type X₂ (R')Si(C_(n) H_(2n+1))

X=Cl, Br

R'=alkyl, such as e.g. methyl-, ethyl-, n-propyl-, i-propyl-, butyl--

n=1-20

(e) Halogenorganosilanes of the type X(R')₂ Si(C_(n) H_(2n+1))

X=Cl, Br

R'=alkyl, such as e.g. methyl-, ethyl-, n-propyl-, i-propyl-, butyl--

n=1-20

(f) Organosilanes of the type (RO)₃ Si(CH₂)_(m) --R'

R=alkyl, such as methyl-, ethyl-, propyl--

m=0, 1-20

R'=methyl-, aryl (e.g. --C₆ H₅, substituted phenyl groups)

--C₄ F₉, OCF₂ --CHF--CF₃, --C₆ F₁₃, --O--CF₂ --CHF₂

--NH₂, --N₃, --SCN, --CH═CH₂,

--OOC(CH₃)C═CH₂

--OCH₂ --CH(O)CH₂ ##STR2## --NH--COO--CH₃, --NH--COO--CH₂ --CH₃, --NH--(CH₂)₃ Si(OR)₃

--S_(x) --(CH₂)₃ Si(OR)₃

(g) Organosilanes of the type (R")_(x) (RO)_(y) Si(CH₂)_(m) --R' ##EQU1## R'=methyl-, aryl (e.g. --C₆ H₅, substituted phenyl groups) --C₄ F₉, OCF₂ --CHF--CF₃, --C₆ F₁₃, --O--CF₂ --CHF₂

--NH₂, --N₃, --SCN, --CH═CH₂,

--OOC(CH₃)C═CH₂

--OCH₂ --CH(O)CH₂ ##STR3## --NH--COO--CH₃, --NH--COO--CH₂ --CH₃, --NH--(CH₂)₃ Si(OR)₃

--S_(x) --(CH₂)₃ Si(OR)₃

(h) Halogenorganosilanes of the type X₃ Si(CH₂)_(m) --R'

X=Cl, Br

m=0, 1-20

R'=methyl-, aryl (e.g. --C₆ H₅, substituted phenyl groups)

--C₄ F₉ OCF₂ --CHF--CF₃, --C₆ F₁₃, --O--CF₂ --CHF₂

--NH₂, --N₃, --SCN, --CH═CH₂,

--OOC(CH₃)C═CH₂

--OCH₂ --CH(O)CH₂ ##STR4## --NH--COO--CH₃, --NH--COO--CH₂ --CH₃, --NH--(CH₂)₃ Si(OR)₃

--S_(x) --(CH₂)₃ Si(OR)₃

(i) Halogenorganosilanes of the type (R)X₂ Si(CH₂)_(m) --R'

X=Cl, Br

R=alkyl, such as methyl-, ethyl-, propyl--

m=0, 1-20

R'=methyl-, aryl (e.g. --C₆ H₅, substituted phenyl groups)

--C₄ F₉, OCF₂ --CHF--CF₃, --C₆ F₁₃, --O--CF₂ --CHF₂

--NH₂, --N₃, --SCN, --CH═CH₂,

--OOC(CH₃)C═CH₂

--OCH₂ --CH(O)CH₂ ##STR5## --NH--COO--CH₃, --NH--COO--CH₂ --CH₃, --NH--(CH₂)₃ Si(OR)₃,

--S_(x) --(CH₂)₃ Si(OR)₃

(j) Halogenorganosilanes of the type (R)₂ X Si(CH₂)_(m) --R'

X=Cl, Br

R=alkyl

m=0, 1-20

R'=methyl-, aryl (e.g. --C₆ H₅, substituted phenyl groups)

--C₄ F₉, OCF₂ --CHF--CF₃, --C₆ F₁₃, --O--CF₂ --CHF₂

--NH₂, --N₃, --SCN, --CH═CH₂,

--OOC(CH₃)C═CH₂

--OCH₂ --CH(O)CH₂ ##STR6## --NH--COO--CH₃, --NH--COO--CH₂ --CH₃, --NH--(CH₂)₃ Si(OR)₃

--S_(x) --(CH₂)₃ Si(OR)₃

(k) Silazanes of the type ##STR7## R=alkyl R'=alkyl, vinyl

(1) Cyclic polysiloxanes of the type D 3, D 4, D 5 in which D 3, D 4 and D 5 signify cyclic polysiloxanes with 3, 4 or 5 units of the type --O--Si(CH₃)₂ --, e.g. octamethylcyclotetrasiloxane=D 4 ##STR8## (m) polysiloxanes or silicone oils of the type ##STR9## R=alkyl such as C_(n) H_(2n+1) in which n=1 to 20, aryl such as phenyl- and substituted phenyl groups, (CH₂)_(n) --NH₂, H

R'=alkyl such as C_(n) H_(2n+1) in which n=1 to 20, aryl such as phenyl- and substituted phenyl groups, (CH₂)_(n) --NH₂, H

R"=alkyl such as C_(n) H_(2n+1) in which n=1 to 20, aryl such as phenyl- and substituted phenyl groups, (CH₂)_(n) --NH₂, H

R'"=alkyl such as C_(n) H_(2n+1) in which n=1 to 20, aryl such as phenyl- and substituted phenyl groups, (CH₂)_(n) --NH₂, H

Further subject matter of the invention is constituted by a method of producing the surface-modified, pyrogenically produced mixed oxides in accordance with the invention which is characterized in that two or more metal chlorides of the series SiCl₄, AlCl₃, TiCl₄, ZrCl₄, FeCl₃, NbCl₅, VOCl₃, WOCl₄, WCl₆, SnCl₄ and GeCl₄ are evaporated [vaporized] together or separately, transferred together with an inert gas, e.g. nitrogen, into the mixing chamber of a known burner, mixed there with hydrogen, air and/or oxygen, the multi-component mixture burned in a reaction chamber, the solid mixed oxides separated thereafter from the gaseous reaction products and optionally freed in moist air from adhering hydrogen chloride and the pyrogenically produced mixed oxides placed in a suitable mixing container, the mixed oxides sprayed under intensive mixing optionally with water at first and then with the surface-modifying reagent or the mixture of several surface-modifying reagents, mixed again 15 to 30 minutes and subsequently tempered at a temperature of 100 to 400° C. for a period of 1 to 6 hours.

The water used can be acidified with an acid, e.g. hydrochloric acid, from pH 7 to 1. The surface-modifying reagent used can be dissolved in a suitable solvent such as e.g. ethanol. The mixing and/or tempering can be carried out in an atmosphere of protective gas such as, for example, nitrogen.

Further subject matter of the invention constitutes a method of producing the surface-modified, pyrogenically produced mixed oxides which is characterized in that two or more metal chlorides from the series SiCl₄, AlCl₃, TiCl₄, ZrCl₄, FeCl₃, NbCl₅, VOCl₃, WOCl₄, WCl₆, SnCl₄ and GeCl₄ are evaporated [vaporized] together or separately, transferred together with an inert gas, e.g. nitrogen, into the mixing chamber of a known burner, mixed there with hydrogen, air and/or oxygen. The multi-component mixture is burned in a reaction chamber, the solid mixed oxides separated thereafter from the gaseous reaction products and optionally freed in moist air from adhering hydrogen chloride and mixed as homogeneously as possible with organohalogen silanes with the exclusion of oxygen, the mixture heated together with slight amounts of water vapor and optionally together with an inert gas in a continuous process [continuous-current process which takes place in a continuous manner] in an upright treatment space designed as a tubular oven to temperatures of 200 to 800° C., preferably 400 to 600° C., the solid and gaseous reaction products separated from each other and the solid products optionally deacidified and dried.

Further subject matter of the invention constitutes the use of the surface-modified, pyrogenically produced mixed oxides in accordance with the invention as

Reinforcement filler in silicone rubber and gum,

Charge stabilizer and flow aid in toner powder,

Free-flow agent,

Anti-blocking aid, e.g. in foils,

UV blocker, e.g. in cosmetics,

Thickening agent, e.g. in paints.

DETAILED DESCRIPTION OF THE INVENTION Examples

Examples for the Production of Mixed Oxides

Metal chlorides 1 and 2 are volatilized in separate evaporators and the chloride vapors conducted by means of nitrogen into the mixing chamber of a burner. There they are mixed with hydrogen and dried air and/or oxygen and burned in a reaction chamber. The reaction products are cooled down to approximately 110° C. in the coagulation zone and the mixed oxides produced are subsequently separated off with a filter. Adhering chloride is removed by treating the powders with moist air at temperatures between 500 and 700° C.

The reaction conditions and the product qualities for the various mixed oxides are collated in table 1.

Examples for the Production of Surface-Modified Mixed Oxides

The reaction conditions and stoichiometric ratios for the surface modification are shown in table 2. The physico-chemical data are collated in table 3.

                                      TABLE 1                                      __________________________________________________________________________     Reaction conditions and product qualities of a few mixed oxides                Mixed       Metal                                                                              Metal         Tapped                                                                             Loss on                                                                            Chloride                                 oxide                                                                              Oxide 1                                                                            Oxide 2                                                                            chloride                                                                           chloride                                                                           H.sub.2                                                                           Air                                                                               BET density                                                                            ignition                                                                           content                                  example                                                                            (wt. %)                                                                            (wt. %)                                                                            1 (g/h)                                                                            2 (g/h)                                                                            (l/h)                                                                             (l/h)                                                                             (m.sup.2 /g)                                                                       (g/l)                                                                              (%) (%)                                      __________________________________________________________________________     1   SiO.sub.2                                                                          TiO.sub.2                                                                          SiCl.sub.4                                                                         TiCl.sub.4                                                                         470                                                                               3280                                                                              95  85  0.6 0.1                                          7.5 92.5                                                                               50  516                                                            2   Al.sub.2 O.sub.3                                                                   SiO.sub.2                                                                          AlCl.sub.3                                                                         SiCl.sub.4                                                                         300                                                                               1300                                                                              179 104 2.9 0.12                                         15  85  126 778                                                            3   Fe.sub.2 O.sub.3                                                                   TiO.sub.2                                                                          FeCl.sub.3                                                                         TiCl.sub.4                                                                         525                                                                               3079                                                                              53  175 1.2 0.3                                          2   98  29  1697                                                           4   Fe.sub.2 O.sub.3                                                                   TiO.sub.2                                                                          FeCl.sub.3                                                                         TiCl.sub.4                                                                         525                                                                               3079                                                                              46  185 1.7 0.4                                          7   93  107 1613                                                           5   SiO.sub.2                                                                          ZrO.sub.2                                                                          SiCl.sub.4                                                                         ZrCl.sub.4                                                                         800                                                                               2420                                                                              121 48  0.9 0.24                                         87  13  1303                                                                               135                                                            6   Al.sub.2 O.sub.3                                                                   TiO.sub.2                                                                          AlCl.sub.3                                                                         TiCl.sub.4                                                                         448                                                                               1276                                                                              47  329 0.7 0.16                                         11  89  188 793                                                            7   Al.sub.2 O.sub.3                                                                   TiO.sub.2                                                                          AlCl.sub.3                                                                         TiCl.sub.4                                                                         525                                                                               3579                                                                              72  120 1.1 0.6                                          25  75  464 1269                                                           8   TiO.sub.2                                                                          ZrO.sub.2                                                                          TiCl.sub.4                                                                         ZrCl.sub.4                                                                         525                                                                               3080                                                                              59  218 0.9 0.15                                         95  5   1661                                                                               78                                                             __________________________________________________________________________

                                      TABLE 2                                      __________________________________________________________________________                         Modifying                                                                            Amount of                                                                            Amount of                                                          reagent                                                                              water solvent                                                                              Tempering                                                                           Tempering                                      Mixed                                                                              Modifying                                                                           (g/100 g                                                                             (g/100 g                                                                             (g/100 g                                                                             time temperature                         Example                                                                             Designation                                                                          oxide                                                                              reagent*                                                                            mixed oxide)                                                                         mixed oxide)                                                                         mixed oxide)                                                                         (h)  (° C.)                       __________________________________________________________________________      9   VT 772                                                                               4   1    10    0     0     4    140                                 10   VT 773                                                                               4   2    10    0     0     2    120                                 11   VT 774                                                                               4   3    10    0     0     2.5  250                                 12   VT 816                                                                               3   1    10    0     0     3    180                                 13   VT 817                                                                               3   2    10    0     0     2    120                                 14   VT 818                                                                               3   3    10    0     0     2.5  250                                 15   VT 775                                                                               2   1    20    0     0     4    140                                 16   VT 776                                                                               2   2    16    0     0     2    120                                 17   VT 777                                                                               2   3    15    0     0     2    250                                 18   VT 819                                                                               8   1    10    0     0     4    180                                 19   VT 820                                                                               8   2    10    0     0     2    120                                 20   VT 821                                                                               8   3    10    0     0     2.5  250                                 21   VT 900                                                                               4   2    12    5     0     2.5  140                                 22   VT 901                                                                               3   2    10    0      10** 2.5  140                                 23   VT 747                                                                               6   2     5    0     0     2    129                                 24   VT 748                                                                               6   2    10    0     0     2    120                                 25   VT 749                                                                               6   4    10    0     0     2    120                                 26   VT 750                                                                               7   2    10    0     0     2    120                                 27   VT 751                                                                               7   4    10    0     0     2    120                                 28   VT 719                                                                               5   1    10    5     0     3    130                                 29   VT 734                                                                               1   3    10    0     0     2    250                                 __________________________________________________________________________      Footnotes to Table 2:                                                          *1 = hexamethyldisilazane = (CH.sub.3).sub.3 Si--NH--Si(CH.sub.3).sub.3         2 = trimethoxyoctylsilane = (CH.sub.3 O).sub.3 Si--(CH.sub.2).sub.7           --CH.sub.3                                                                     ##STR10##                                                                       4 = trimethoxypropylsilane = (CH.sub.3 O).sub.3 Si--CH.sub.2 --CH.sub.2       --CH.sub.3 -                                                                   ** = ethanol                                                             

                                      TABLE 3                                      __________________________________________________________________________                Specific                                                                       surface                                                                              Tapped    Loss of Carbon                                                 according to                                                                         density                                                                            Drying loss                                                                          ignition                                                                               content                                     Example                                                                             Designation                                                                          BET (m.sup.2 /g)                                                                     (g/l)                                                                              (%)   (%) pH  (%)                                         __________________________________________________________________________      9   VT 772                                                                               40    269 0.0   1.3 6.4 0.5                                         10   VT 773                                                                               36    280 0.1   4.7 3.4 3.6                                         11   VT 774                                                                               27    301 0.2   3.9 3.4 2.7                                         12   VT 816                                                                               45    258 0.4   1.1 7.5 0.5                                         13   VT 817                                                                               39    288 0.7   3.9 3.4 3.5                                         14   VT 818                                                                               32    292 0.0   3.6 3.6 2.9                                         15   VT 775                                                                               124   127 0.5   3.4 6.6 1.7                                         16   VT 776                                                                               111   136 1.0   9.5 4.2 5.8                                         17   VT 777                                                                               101   136 0.9   4.7 4.2 2.9                                         18   VT 819                                                                               51    245 0.5   0.7 9.0 0.4                                         19   VT 820                                                                               45    275 0.0   4.4 4.0 3.6                                         20   VT 821                                                                               35    275 0.0   2.3 4.1 2.5                                         21   VT 900                                                                               34    275 0.1   4.9 3.5 3.9                                         22   VT 901                                                                               38    282 0.6   4.0 3.6 3.6                                         23   VT 747                                                                               31    396 0.2   1.7 3.7 2.0                                         24   VT 748                                                                               23    409 0.3   4.8 4.0 3.9                                         25   VT 749                                                                               26    402 0.3   2.3 4.1 1.8                                         26   VT 750                                                                               56    161 0.3   16.8                                                                               3.8 3.9                                         27   VT 751                                                                               55    162 0.2   2.7 4.1 2.0                                         28   VT 719                                                                               60     60 0.1   1.1 6.4 1.3                                         29   VT 734                                                                               74    114 0.5   2.5 4.2 2.5                                         __________________________________________________________________________ 

What is claimed is:
 1. Surface-modified, pyrogenically produced mixed oxides which contain two or more components from the series consisting of SiO₂, Al₂ O₃, TiO₂, ZrO₂, Fe₂ O₃, Nb₂ O₅, V₂ O₅, WO₃, SnO₂, and GeO₂ which have been freed from adhering hydrogen chloride in moist air and do not undergo a drying step prior to hydrophobing and were surface-modified with one or more compounds of the following groups:(a) Organosilanes of the formula (RO)₃ Si(C_(n) H_(2n+1))R=alkyl n=1-20 (b) Organosilanes of the formula R'_(x) (RO)_(y) Si(C_(n) H_(2n+1))R=alkyl R'=alkyl n=1-20 x+y=3 x=1, 2 y=1, 2 (c) Halogenorganosilanes of the formula X₃ Si(C_(n) H_(2n+1))X=Cl, Br n=1-20 (d) Halogenorganosilanes of the formula X₂ (R')Si(C_(n) H_(2n+1))X=Cl, Br R'=alkyl n=1-20 (e) Halogenorganosilanes of the formula X(R')₂ Si(C_(n) H_(2n+1))X=Cl, Br R'=alkyl n=1-20 (f) Organosilanes of the formula (RO)₃ Si(CH₂)_(m) --R'R=alkyl m=0, 1-20 R'=methyl-, aryl --C₄ F₉, OCF₂ --CHF--CF₃, --C₆ F₁₃, --O--CF₂ --CHF₂ --NH₂, --N₃, --SCN, --CH═CH₂, --OOC(CH₃)C═CH₂, --OCH₂ --CH(O)CH₂, ##STR11## --NH--COO--CH₃, --NH--COO--CH₂ --CH₃, --NH--(CH₂)₃ Si(OR)₃ (g) Organosilanes of the formula (R")_(x) (RO)_(y) Si(CH₂)_(m) --R' ##EQU2## R'=methyl-, aryl --C₄ F₉, OCF₂ --CHF--CF₃, --C₆ F₁₃, --O--CF₂ --CHF₂ --NH₂, --N₃, --SCN, --CH═CH₂, --OOC(CH₃)C═CH₂ --OCH₂ --CH(O)CH₂ ##STR12## --NH--COO--CH₃, --NH--COO--CH₂ --CH₃, --NH--(CH₂)₃ Si(OR)₃ (h) Halogenorganosilanes of the formula X₃ Si(CH₂)_(m) --R'X=Cl, Br m=0, 1-20 R'=methyl-, aryl --C₄ F₉, OCF₂ --CHF--CF₃, --C₆ F₁₃, --O--CF₂ --CHF₂ --NH₂, --N₃, --SCN, --CH═CH₂, --OOC(CH₃)C═CH₂ --OCH₂ --CH(O)CH₂ ##STR13## --NH--COO--CH₃, --NH--COO--CH₂ --CH₃, --NH--(CH₂)₃ Si(OR)₃ (i) Halogenorganosilanes of the formula (R)X₂ Si(CH₂)_(m) --R'X=Cl, Br R=alkyl m=0, 1-20 R'=methyl-, aryl --C₄ F₉, OCF₂ --CHF--CF₃, --C₆ F₁₃, --O--CF₂ --CHF₂ --NH₂, --N₃, --SCN, --CH═CH₂, --OOC(CH₃)C═CH₂ --OCH₂ --CH(O)CH₂ ##STR14## --NH--COO--CH₃, --NH--COO--CH₂ --CH₃, --NH--(CH₂)₃ Si(OR)₃ (j) Halogenorganosilanes of the formula (R)₂ X Si(CH₂)_(m) --R'X=Cl, Br R=alkyl m=0, 1-20 R'=methyl-, aryl --C₄ F₉, OCF₂ --CHF--CF₃, --C₆ F₁₃, --O--CF₂ --CHF₂ --NH₂, --N₃, --SCN, --CH═CH₂, --OOC(CH₃)C═CH₂ --OCH₂ --CH(O)CH₂ ##STR15## --NH--COO--CH₃, --NH--COO--CH₂ --CH₃, --NH--(CH₂)₃ Si(OR)₃ (k) Silazanes of the formula ##STR16## R=alkyl R'=alkyl, vinyl (l) Cyclic polysiloxanes of the formula D 3, D 4, D 5, ##STR17## (m) polysiloxanes or silicone oils of the formula ##STR18## R=alkyl, aryl, (CH₂)_(n) --NH₂, H R'=alkyl, aryl, (CH₂)_(n) --NH₂, HR"=alkyl, aryl, (CH₂)_(n) --NH₂, H R'"=alkyl, aryl, (CH₂)_(n) --NH₂, H , wherein n=1-20.
 2. Surface-modified, pyrogenically produced mixed oxides according to claim 1 which have been sprayed with additional water prior to hydrophobing.
 3. A process for the preparation of surface-modified, pyrogenically produced mixed oxides according to claim 1, wherein two or more metal chlorides selected from the group consisting of SiCl₄, AlCl₃, TiCl₄, ZrCl₄, FeCl₃₁, NbCl₅, VOCl, WoCl₄, WCl₆, SnCl₄, and GeCl₄ are evaporated together or separately, transferred together with an inert gas into the mixing chamber of a known burner, mixed there with hydrogen, air and/or oxygen, the multi-component mixture is burned in a reaction chamber, the solid mixed oxides are then separated from the gaseous reaction products and freed from adhering hydrogen chloride in moist air, and the progenically produced mixed oxides are charged to a suitable mixing vessel, the mixed oxides are aprayed, with intensive mixing, and subsequently with the surface-modifying reagen or the mixture of several surface-modifying reagents, mixed agin for 15 to 30 minutes and subsequently heat-treated at a temperature of 100 to 400° C. for a period of 1-6 hours.
 4. A process for the preparation of surface-modified, pyrogenically produced mixed oxides according to claim 1, wherein two or more metal chlorides selected from the group consisting of SiCl₄, AlCl₃, TiCl₄, ZrCl₄, FeCl₃, NbCl₅, VOCl, WoCl₄, WCl₆, SnCl₄, and GeCl₄ are evaporated together or separately, transferred together with an inert gas into the mixing chamber of a known burner, mixed there with hydrogen, air and/or oxygen, the multi-component mixture is burned in a reaction chamber, the solid mixed oxides are then separated from the gaseous reaction products and freed from adhering hydrogen chloride in moist air, and mixed as homogeneously as possible with organohalogen silanes with the exclusion of oxygen, and the mixture together with small quantities of water vapor and optionally together with an inert gas is heated to temperatures from 200 to 800° C., in the continuous co-current process in a treatment chamber having the form of an upright tubular furnace, the solid and gaseous reaction products are separated from each other, and the solid products are deacidified and dried.
 5. The process of claim 4 wherein the temperature is 400 to 600° C.
 6. The process according to claim 3 which further comprises the step of spraying with additional water prior to hydrophobing.
 7. The process according to claim 4 which further comprises the step of spraying with additional water prior to hydrophobing.
 8. The process according to claim 5 which further comprises the step of spraying with additional water prior to hydrophobing.
 9. A surface-modified, pyrogenically produced mixed oxide according to claim 1 in the form of a reinforcing filler in silicone rubber or rubber, a charge stabilizer or free-flow agent in a toner powder, a free-flow agent, an anti-blocking agent, a UV blocker, or a thickener. 